Here is what you all need:
A clear base coat, nail polish, topcoat, glass cabochons, cabochon trays or jewelry bails, heavy-duty glue, nail polish remover and q-tips or cotton.
Step 1: Paint the back of the cabochons with a layer of clear polish or base coat. Be sure that your base coat does not have any color, this needs to be perfectly clear. This will even out any flaws in your glass before you start painting with the colors. Wait until this coat is absolutely dry before moving on to step two.
Step 2: If you are using a crackle polish, add a layer to the glass now. Here I used OPI Silver Shatter. It goes on normally, but as it dries. I'm not really a fan of this look on my nails but I think this looks fabulous on this pendant. Wait for this to dry, and move on to the next step.
Step 3: Start to layer your nail polish. On the left, I'm using Zoya Roxy, a deep purple with tons of purple glitter. On the right, I'm layering Butter London Bluey over the shatter.
Keep building the layers until it's at the opacity you like. It might take just one or two coats, or in the case of some clear glitters, as many as five or six. Be sure the polish is dry between layers.
Note: if you drip down the sides or generally make an error, you can try to correct it with the remover and q-tips. Or, if you accidentally flip your still-wet project over so it lands face down on your working surface, you can start over entirely by removing the polish.
Step 4: When you've built up the layers to your satisfaction, add a layer of topcoat. This is especially important if you are not setting the pendant in a tray, but just adding the jewelry bail. This will help protect the polish.
Step 5: Once the top coat is dry, it's time to glue. I use E6000 is very strong, and dries clear, so it won't alter the look of the colors. For the tray setting, smooth the glue in a thin layer evenly over the back of the cabochon, and place in the tray. For the bail, add a touch of glue to the back of the bail, and center it along the top of the glass.
Step 6: Let the glue dry. Done!